1. Field of the Invention
The instant disclosure relates to a photomask cleaning method and system; in particular, to a photomask cleaning method and system that cleans photomasks through rinsing and wiping.
2. Description of Related Art
IC chip is composed of highly precise integrated circuits, in which the manufacturing process requires the use of high precision machines on silicon wafer for high precision lamination in a clean room environment. The manufacturing cost for the associated machine and fabrication plant is high. Thus, in silicon wafer manufacturing process, product yield rate can determine if a semiconductor factory profits or not. Therefore, improving product yield is the one of the most important factor in the minds of every semiconductor factory owner.
One of the major factors that affects yield rate of wafers is the cleanliness of the photomask. If contaminated photomasks are used to produce semiconductors during photolithography process, corresponding defects can develop on the wafer. In order to keep the photomask clean, photomasks are usually setup with a photomask protective film (Pellicle) to prevent dust particles from attaching to the mask. Since the photomask protective film is kept a certain distance away from the photomask through a frame structure, dust particles may collect on the photomask protective film such that focusing issues during development can be prevented.
It is a common practice that, prior to photomask shipment or micro-film processing, a scan is conducted to confirm that the pattern on the photomask is accurate. If flaws are identified, they must be removed or the photomask protective film must be scrapped off the photomask, and then immersed into an acid bath for cleaning. For cleaning solutions, sulfuric acid along with hydrogen peroxide solution (H2SO4/H2O2, SPM), and the aqueous solution of ammonium hydroxide along with hydrogen peroxide (SCL) solution are commonly used. Sulfuric acid and hydrogen peroxide solution are used to remove large organic molecules while ammonium hydroxide and hydrogen peroxide aqueous solution are used to remove small organic molecules and particles. Successively, deionized water (DI water) is used to remove residual cleaning solution to complete the cleaning process. Thereafter, a new photomask protective film is disposed onto the photomask. However, the photomask protective film is quite expensive, thus scraping sheets of protective films will significantly increase the costs of photomasks application. Furthermore, the adhesive on the common photomask protective film is generally composed of ester structure (RCOOR) x such as poly-acrylic ester structure. Thus, when photomasks are immersed into a bath of sulfuric acid and hydrogen peroxide solution, (RCOOR) x will hydrolyze into a colloidal state of (RCOOH) x which may cause defects on the photomask pattern and lead to scrapping. In fact, each photomask can only be used to clean three times before scrapping while the price of photomasks can be as high as hundreds of thousands of dollars up to 2 million dollars, and rendering the cost of photomask application high.
To improve upon from the conventional method, one possible method to improve photomask cleanliness is to clamp and move the photomask towards cleaning and drying equipment for cleaning and drying.
To address the above issues, the inventor strives via associated experience and research to present the instant disclosure, which can effectively improve the limitation described above.